Injection molded articles are used for a variety of purposes. Plastic injection molded products are commonly made from materials such as polyethylene terephthalate (PET) or polypropylene (PP). In the case of articles 10 such as shown in FIG. 1 that have non-symmetric shapes (relative to the location of the injection gate 15), a flow leader 20, e.g., a local increase in thickness from the nominal part thickness, are used to compensate for the differences in mold flow lengths in different directions from the injection gate 15.
Plastic materials such as PET and PP are gas (e.g., oxygen, nitrogen, etc.) permeable. For applications in which gas permeability is undesirable, for example, food products, medicines and other substances and products that degrade upon gaseous exposure, a barrier material is co-injected with the plastic material. Typically, the barrier material, such as Ethyl Vinyl Alcohol (EVOH), is injected at the interior of the PET/PP material stream, forming an EVOH interior layer in the molded product.
The present inventor has attempted to form non-symmetric co-injection molded containers containing such an interior layer using known non-symmetric molding technologies, e.g., utilizing a flow leader, yet the resulting articles do not exhibit sufficient gas-impermeability. The inventor has found that when using conventional flow leader technologies, the interior layer does not sufficiently extend throughout the molded product to prevent detrimental gas permeation. Even when only small areas of the article do not contain the barrier material or a sufficiently thick barrier material, substantial permeation occurs.